Method for elimination of reversal reexposure in processing photographic films



nite States Richard W. HEHH,

Bard, Rochester, (Iompany, Jersey No Drawing. Filed Nov. 29, 1957, Ser.No. 699,478 3 Claims. (Cl. 96-59) David K. Bulloch, and Charleton C.N.Y., assignors to Eastman Kodak Rochester, N.Y., a corporation of NewThis invention relatesto an improved method of photographic processing,and more particularly, to the reversal processing of photographic silverhalide emulsions.

' It is known that photographic silver halide emulsions for producingblack-and-white images can be reversal processed by subjecting theexposed emulsions to conventional development, followed by bleaching,clearing, and reversal re-exposure, followed by a subsequent developmentstep. Also, it is known that in the processing of the photographicsilver halide emulsions of color films, the exposed emulsions can besubjected to conventional black-and-white development, followed byreversal exposure and subsequent color development. Both of theseprocesses require that the exposed silver halide emulsions, after afirst development, be given a subsequent reversal exposure before anyfurther development can take place to produce the desired positiveimage.

Accordingly, it is an object of our invention to provide a method ofeliminating the re-exposure required in blackand-white processing byreversal, as well as in certain color processing. Another object is toprovide a method of color processing which not only eliminates reversalreexposure, but also provides more accurate rendition of the colors inthe original. Other objects will become apparent from a consideration ofthe following description and examples.

According to the method of our invention, the reversal re-exposure forthe processing of black-and-white or color reproductions can beeliminated by treating the photographic silver halide emulsions after afirst (negative) development with a solution containing an alkali metal(e.g., sodium, potassium, etc.) borohydride.

In the reversal processing of photographic silver halide emulsions forproducing black-and-White images, the emulsions are exposed in thecustomary manner and given a first development in an ordinaryphotographic silver halide developer. The developed films are thenWashed and given a bleaching treatment in an ordinary photographicbleach bath containing an oxidizing agent, such as permanganate,dichromate, etc. After bleaching, the film is again washed andtreated ina clearing bath, after which the film is again rinsed. Treatment of thefilm with an alkali metal borohydride aqueous solution produces apositive image, free from stain, without any exposure to light. Ifdesired, the concentration of the alkali metal borohydride solution canbe controlled so that no image is produced directly. Then, the treatedemulsion can be given a conventional development which rapidly producesthe desired positive image. The concentration of the alkali metalborohydride in the treating solution can vary depending upon whether itis desired to produce an image directly without any subsequentdevelopment, or Whether it is desired to use a second development in aconventional photographic developer. In general, the concentration ofthe alkali metal borohydride can vary from about 0.1 g./liter toconcentrations as high as 30 g./.liter. While more concentratedsolutions 2,984,567 Patented May 16, .1961

can be employed to produce-an image directly without any subsequentdevelopment, there is generally no advantage in doing so.

For the processing of color films by reversal, it is .apparent that nobleaching or clearing baths should be used after the first development,since color formation is accomplished by reversal re-exposure of theresidual silver halide and subsequent treatment with a color developerwhich undergoes a coupling reaction vn'th color-forming components orcouplers, which can be present either in the developer itself or mostadvantageously, in the photographic silver halide emulsion layers. Inthose cases where the color-forming components or couplers are presentin the photographic developers, it is apparentthat the alkali metalborohydride treatment should not be used until immediately prior to thelast color development step, inasmuch as the alkali metal borohydridewill nucleate all silver halide which has not been exposed ariddeveloped previously. For example, in processing color films of theKodachrome type, it is possible to use the alkali metal borohydridetreatment immediately prior to the last color development step and tothus eliminate the re-exposure preceding that step. This treatment hasbeen found to be far more elfective than reversal re-exposure withintensive light sources, which have an insufiicient effect on theremaining silver halide to provide accurate color development for thelast step of the processing. Since the silver halide emulsion layershave already undergone extensive treatment and development in stronglyalkaline solutions, the remaining silver halide has either beeninadequately exposed during the last reversal re-exposure, or thesensitizing dyes and other emulsion addenda have been diminished ineffectivenessby the extensive processing. Our treatment with alkalimetal borohydrides causes the silver halides to become nucleated almostinstantaneously so that color development can then be completed bydeveloping in a conventional color developer without any intensivere-exposure.

Particularly useful color films for reversal processing according to themethod of our invention. are films comprising a conventional support,such as cellulose esters, glass, polyester film, polyvinyl acetal film,polycarbonate film, etc., having coated thereon at least two silverhalide layers which have been sensitized to particular regions of thespectrum. These emulsions have incorporated therein the color-formingcomponents or couplers, which combine with the oxidation products of thephotographic color developers, to produce the desired color images. Forexample, a typical color film, useful in practicing our inventioncomprises a support having coated thereon a red-sensitized photographicsilver halide emulsion having incorporated therein a coupler for thecyan image (e.g., a phenolic coupler), a green-sensitized photographicsilver halide emulsion having incorporated therein a coupler for themagenta image (e.g., pyrazolone coupler), and a blue-sensitizedphotographic silver halide emulsion containing a coupler for the yellowimage (cg, a coupler containing an open-chain ketomethylene group). Thephotographic element can also contain conventional interlayers andfilter layers, such as a yellow filter layer beneath the blue-sensitizedemulsion to prevent exposure by blue light to either the redorgreen-sensitized emulsion. Photographic color films of theabove-described type can be processed by a technique requiring fewersteps than the processing of color films of the Kodachrome typementioned above. For the processing of the emulsions having couplercompounds incorporated therein, it is only necessary to treat theexposed color film with the usual type of black-and-white developer forproducing a negative silver image, followed by treatment with the alkalimetal borohydride solutions herein described to nucleate the residualsilver halide, which can then be developed with one of the conventionalcolor developers.

The following examples will serve to illustrate more fully the manner ofpracticing our invention.

Example 1 An ordinary photographic silver halide emulsion, such as KodakPlusX 16 mm. Reversal Film was exposed to a step wedge in an EastmanType Ib sensitometer and then developed for 3 minutes in a developerhaving the following composition:

Water to make 1 liter.

The developed film was then rinsed thoroughly with water and bleachedfor 2 minutes in a composition having the following formula:

Potassium bichromate g 9.4 Sulfuric acid cc 12.0 Water to make 1 liter.

Example 2 A photographic multi-layer color element containing threedifferentially sensitized photographic silver halide emulsion layers,having color-forming agents or couplers incorporated therein, wasexposed in the usual manner to a subject. The exposed color film wasthen developed in a developer having the following composition:

Sodium hexametaphosphate g 2.0 N-methyl-p-aminophenol sulfate g 6.0Sodium sulfite, anhydrous g 50.0 Hydroquinone g 6.0 Sodium carbonatemonohydrate g 35.0 Potassium bromide g 2.0 Sodium thiocyanate g 1.5 0.5%solution of 6-nitrobenzimidazole nitrate cc 12.0

0.1% solution of potassium iodide cc 10.0 Water to make 1 liter.

The element was then thoroughly washed with water and treated in ahardening bath having the following composition:

Potassium chrome alum crystals g 30.0 Water to make 1 liter.

The element was then thoroughly washed with water and treated for 30seconds ina solution having the following composition:

G. Sodium borohydride 0.25 Sodium hydroxide 4.0

Water to make 1 liter.

The element was then treated in a color developer having the followingcomposition:

Benzyl alcohol cr- Sodium hexarnetaphosphate g 4 Sodium sulfite,anhydrous g 5.0 Trisodium phosphate g 40.0 Potassium bromide g 0.25 0.1%solution of potassium iodide cc 10.0 Sodium hydroxide g 6.5 Colordeveloper g 11.33 Ethylenediamine sulfate g 7.8 Citrazinic acid g 1.5

Water to make 1 liter.

l-amino-N-ethyl-N (B methanesulfonamidoethyl) m toluidine sesquisulfatemonohydrate. The element was then thoroughly washed with water andtreated in a clearing and fixing bath having the following composition:

G. Sodium thiosulfate 150.0 Sodium bisulfite 20.0

Water to make 1 liter.

The element was then treated in a bleach bath having the followingcomposition:

G. Potassium dichromate 5.0 Potassium ferricyanide 70.0 Potassiumbromide 20.0

Water to make 1 liter.

The element was again washed and treated once again with the clearingand fixing bath identified above. The element was again washed andtreated in a stabilizing bath having the following composition:

Formaldehyde (37% by weight) cc 7.0 Dispersing agent 1 g 0.5 Water tomake 1 liter.

1 Such as Triton-X 100, i.e., an alkylaryl polyether alcohol(octylphenoxy poiyethoxy ethanol).

Photographic color elements which can be processed according to themethod described in Example 2 above include the elements shown inSchinzcl U.S. Patent 2,266,443, issued December 16, 1941, and FierkeU.S. Patent 2,272,191, issued February 10, 1942, for example.Photographic elements, wherein the silver halide emulsions contain thecoupler or color-forming component in dispersed form, have been foundparticularly suitable for the process described in Example 2. It hasbeen found that ordinary processing of such reversal-type filmsfrequently causes a re-reversal effect, particularly in the magneta dyeimage and a density loss in the shoulder region of the reversal exposurescale. By shoulder rereversal, we mean the occurrence of a dye maximumin the reversal scale at some point prior to the no-exposure step of thescale of densities developed in the black-andwhite developer. Thiseffect is believed to be due, at least in part, by inadequate reversalexposure and use of partially exhausted color developer. Use of thealkali metal borohydride solutions of our invention not only eliminatesthe necessity for a reversal exposure, but it also materially improvesdye formation in the magenta layer.

Example 3 A photographic silver chlorobromide emulsion was exposed to astep wedge in the usual manner and then developed for about 2 minutes ina developer for high contrast emulsions, such as a developer having thefollowing composition:

Water to make 1 liter. The exposed film was then bleached for 1 minutein a assess? potassium permanganate bleach containing sodium chlorideand hydrochloric acid as a stain remover. After washing, the film wastreated for about 30 seconds in a 2% sodium bisulfite clearing bath andthen treated with a 1% aqueous solution of potassium borohydride. Animage rapidly appeared. It was free from stain and had a neutral blackcolor.

Development of the exposed photographic silver halide emulsions toproduce a black-and-white negative image as described in the foregoingexamples can be accomplished using any of the conventional developerscustomarily employed in photographic art for producing black-and-whitenegative images. Such developers include compounds known aspolyhydroxybenzenes (e.g., hydroquinone, catechol, pyrogallol, etc.) andN-substituted aminophenols (e.g., N-methylaminophenols, N-ethylaminophenols, etc.), or mixtures of such developers. Prominentamong such developing agents for the rapid development of photographicimages are those comprising hydroquinone and Elon developer(N-methylpaminophenol). Instead of using polyhydroxybenzenes, it is alsopossible to use the well known class of developing agents referred to inthe photographic art as 3- pyrazolidones, such as those described inKendall et al. U.S. Patent 2,704,762, issued March 22, 1955.

Color development, as described in the above examples, can be carriedout using any of the well known color-forming developers which arecapable of coupling with the color-forming components or couplers.Particularly useful color-forming developers are the phenylenediaminesand substituted derivatives thereof. Typical of such color-formingdevelopers are the sulfonamidosubstituted p-phenylenediamines disclosedin Weissberger U.S. Patent 2,548,574, issued April 10, 1951, thesubstituted p-phenylenediamines disclosed in Weissberger et al. U.S.Patents 2,552,240-2, issued May 8, 1951, and the substitutedp-phenylenediamines disclosed in Weissberger et al. U.S. Patent2,566,271, issued August 28, 1951. Other phenylenediamine color-formingdevelopers can be employed to like advantage in the process of ourinvention.

The processes for producing direct positive images, as described in theforegoing specification, have been previously described in the priorart, and our invention is not to be limited to any particular method ofprocessing photographic silver halide emulsions according to these wellknown techniques. Rather, our invention resides in the discovery thatalkali metal borohydrides can be employed in the form of their aqueoussolutions to either nucleate silver halides so that silver images can beobtained by known techniques of photographic development, or the silverhalides can be treated for a period of time sufiicient to fogsubstantially all of the residual silver halide so that no subsequentphotographic development is required. The extent of treatment willobviously depend upon the type of film being treated and whether one desires to obtain merely a black-and-white image, or whether one desiresto process a color film to produce subtractively-colored images. The pHof the alkali metal borohydride solutions can be varied to modify theactivity of the alkali metal borohydrides. In general, we have foundthat the pH should advantageously not be allowed to drop below about 10,since these borohydrides become somewhat unstable at too low pH (i.e.,toward acid side of neutrality) values.

Instead of using sodium bisulfite or sodium sulfite as reducing agentsin the direct reversal process for producing black-and-white images, itis possible to use other alkali metal salts, such as those of potassium,etc.

The method of processing color films as herein described is particularlyuseful where the photographic silver halide emulsions are hardened priorto the treatment with the alkali metal borohydride solutions. Wherecolor films are used which have emulsions which have not been previouslyhardened, it is desirable in many cases to '6 harden the emulsion beforetreatment. with the alkali metal borohydride solutions.

While other materials have been used in place of the alkali metalborohydrides of our invention, the nucleating effects are not nearly asuseful as those described herein. For example, hydrazine compounds, suchas phenylhydrazine, l-naphthylhydrazine, p-bromophenylhydrazine, etc.,can be used, though less advantageously than the alkali metalborohydrides of our invention. Other hydrazine compounds which can beused comprise those shown in Ives U.S. Patent 2,588,982, issued March11, 1952. Again, the alkali metal borohydrides of our invention havedistinct advantages over the hydrazine compounds shown in the UnitedStates patent.

What we claim as our invention and desire secured by Letters Patent ofthe United States is:

l. in a photographic reversal process comprising eX- posing aphotographic silver halide emulsion to an im-' age, developing saidphotographic silver halide emulsion to produce a black-and-whitenegative image by contacting said exposed photographic silver halideemulsion with a photographic developer, and subsequently obtaining areversal positive image by contacting said photographic silver halideemulsion with a nucleating agent for a sufficient time only to nucleatepreviously unexposed silver halide substantially without the formationof a visible image, followed by contacting said photographic silverhalide emulsion with a second photographic developer for a suflicienttime to develop a visible image, the step of nucleating saidphotographic silver halide emulsion by contacting said photographicsilver halide emulsion with an aqueous solution of an alkali metalborohydride having a pH of at least 10.0 and containing at least 0.1g./liter of solution but not more than 30 g./liter of solution of analkali metal borohydride selected from the class consisting of sodiumborohydride and potassium borohydride for a sufficient time only tonucleate previously unexposed silver halide substantially without theformation of a visible image.

2. In a method of producing a photographic color reproduction comprisingexposing to a colored image a photographic element containing at leasttwo photographic silver halide emulsion layers which have beendifferentially sensitized to diiferent spectral regions, developing saidphotographic element to a negative blackand-white image by treatmentwith a photographic blackand-white developer, contacting saidphotographic element with a nucleating agent for sufiicient time only tonucleate previously unexposed silver halide substantially without theformation of a visible image, and developing said photographic elementin a photographic color developer in the presence of a color-formingcompound which couples with the oxidation products of said photographiccolor developer to produce a colored image, the step comprisingnucleating said previously unexposed silver halide by contacting saidphotographic element with an aqueous solution of an alkali metalborohydride having a pH of at least 10.0 and containing at least 0.1g./liter of solution but not more than 30 g./liter of solution ot analkali metal borohydride selected from the class consisting of sodiumborohydride and potassium borohydride for a suflicient time only tonucleate said previously unexposed silver halide substantially withoutthe formation of a visible image.

3. In a method of reproducing a photographic color reproductioncomprising exposing to a colored image a photographic element comprisinga support having coated thereon three photographic silver halideemulsion layers, one of said layers being sensitive to the red region ofthe spectrum and having dispersed therein a coupler for producing a cyanimage, one of said layers being sensitive to the green region of thespectrum and containing a coupler for producing a magenta image, and thethird one of said layers being sensitive to the blue region of thespectrum and containing a coupler for producing a 7 yellow image,developing said photographic element in a photographic black-and-whitedeveloper to produce a negative image, contacting said photographicelement with a nucleating agent for a sufiicient time only to nucleatepreviously unexposed silver halide substantially without the formationof a visible image, developing said photographic element in aphotographic phenylenediamine color developer to produce colored imagesbearing a complementary relationship to the color in the original beingproduced, contacting said photographic element with a photographicclearing and fixing solution, contacting said photographic element in anoxidizing bath to remove silver images, and contacting said photographicelement with a clearing and fixing solution to remove residual silversalts from said photographic silver halide emulsion layers, the step ofnucleating said previously unexposed silver halide by contacting saidphotographic element with an aqueous solution of an alkali metalborohydride having a pH of at least 10.0 and containing at least 0.1 g./liter of solution but not more than 30 g./liter of solution of an alkalimetal borohydride selected from the class consisting of sodiumborohydride and potassium borohydride for a suflicient time only tonucleate previously unexposed silver halide substantially without theformation of a visible image.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Mees: The Theory of the Photographic Process,

20 Revised Ed., p. 109, The MacMillan Co., N.Y., 1954;

(Copy in Sci. Lib.)

1. IN A PHOTOGRAPHIC REVERSAL PROCESS COMPRISING EXPOSING A PHOTOGRAPHICSILVER HALIDE EMULSION TO AN IMAGE, DEVELOPING SAID PHOTOGRAPHIC SILVERHALIDE EMULSION TO PRODUCE A BLACK-AND-WHITE NEGATIVE IMAGE BYCONTACTING SAID EXPOSED PHOTOGRAPHIC SILVER HALIDE EMULSION WITH APHOTOGRAPHIC DEVELOPER, AND SUBSEQUENTLY OBTAINING A REVERSAL POSITIVEIMAGE BY CONTACTING SAID PHOTOGRAPHIC SILVER HALIDE EMULSION WITH ANUCLEATING AGENT FOR A SUFFICIENT TIME ONLY TO NUCLEATE PREVIOUSLYUNEXPOSED SILVER HALIDE SUBSTANTIALLY WITHOUT THE FORMATION OF A VISIBLEIMAGE, FOLLOWED BY CONTACTING SAID PHOTOGRAPHIC SILVER HALIDE EMULSIONWITH A SECOND PHOTOGRAPHIC DEVELOPER FOR A SUFFICIENT TIME TO DEVELOP AVISIBLE IMAGE, THE STEP OF NUCLEATING SAID PHOTOGRAPHIC SILVER HALIDEEMULSION BY CONTACTING SAID PHOTOGRAPHIC SILVER HALIDE EMULSION WITH ANAQUEOUS SOLUTION OF AN ALKALI METAL BOROHYDRIDE HAVING A PH OF AT LEAST10.0 AND CONTAINING AT LEAST 0.1 G./LITER OF SOLUTION BUT NOT MORE THAN30 G./LITER OF SOLUTION OF AN ALKALI METAL BOROHYDRIDE SELECTED FROM THECLASS CONSISTING OF SODIUM BOROHYDRIDE AND POTASSIUM BOROHYDRIDE FOR ASUFFICIENT TIME ONLY TO NUCLEATE PREVIOUSLY UNEXPOSED SILVER HALIDESUBSTANTIALLY WITHOUT THE FORMATION OF A VISIBLE IMAGE.